1. Field of the Invention
The present invention relates to an image binarizing apparatus for binarizing multi-value image data which is output from an image taking device.
2. Related Background Art
Binarizing apparatuses have hitherto utilized multi-value image data which is obtained with A/D convertors by converting an analog video signal from image taking devices into a multi-value digital video signal having N-bit gradations. The binarizing apparatus simply binarizes such multi-value image data based on a fixed threshold, or processes it in the following way. A threshold is altered to be suitable for an image, based on surrounding pattern information, such as an isolated spot. The multi-value image data is then binarized so as not to lose information regarding the image. Also, an arithmetic technique, such as differential or integral calculus, is adapted to multi-value image data, which is binarized by the binarizing apparatus by using two-dimensional image filters.
Such a conventional binarizing apparatus, however, has a problem in that an unevenness in an amount equal to one pixel is formed in an edge pattern portion which should have been formed into a straight line, also information regarding fine light and shade patterns is lost.
Furthermore, to pick up information regarding fine light and shade patterns, after an offset voltage has been added to an analog video signal, a signal with a fixed amount of attenuation is delayed to compare it with the original analog video signal. An image data is thus binarized. Such a construction, however, has a serious disadvantage in that a signal which has been binarized is shifted time-wise in accordance with the amount of time during which the attenuated signal is delayed (a pattern position is shifted within an image plane to be taken).